/// <summary>
/// <para>
/// The returned <code>RateLimiter</code> is intended for cases where the resource that actually
/// fulfills the requests (e.g., a remote server) needs "warmup" time, rather than
/// being immediately accessed at the stable (maximum) rate.
/// </para>
/// <para>
/// The returned <code>RateLimiter</code> starts in a "cold" state (i.e. the warmup period
/// will follow), and if it is left unused for long enough, it will return to that state.
/// </para>
/// </summary>
/// <param name="permitsPerSecond">The rate of the returned <code>RateLimiter</code>, measured in how many permits become available per second</param>
/// <param name="warmupPeriod">The duration of the period where the <code>RateLimiter</code> ramps up its rate, before reaching its stable (maximum) rate</param>
/// <param name="unit">The time unit of the warmupPeriod argument</param>
/// <param name="coldFactor"></param>
public static RateLimiter Create(double permitsPerSecond, long warmupPeriod, TimeUnit unit = TimeUnit.Seconds, double coldFactor = 3.0)
{
if (warmupPeriod < 0)
{
throw new ArgumentOutOfRangeException(nameof(warmupPeriod), "WarmupPeriod must not be negative");
}
return(Create(SleepingStopwatch.CreateFromSystemTimer(), permitsPerSecond, warmupPeriod, unit, coldFactor));
}
/// <summary>
/// Creates a <code>RateLimiter</code> with the specified stable throughput, given as "permits per second"
/// </summary>
/// <remarks>
/// Creates a <code>RateLimiter</code> with the specified stable throughput, given as
/// "permits per second" (commonly referred to as QPS, queries per second).
///
/// The returned <code>RateLimiter</code> ensures that on average no more than <code>permitsPerSecond</code>
/// are issued during any given second, with sustained requests
/// being smoothly spread over each second. When the incoming request rate exceeds
/// <code>permitsPerSecond</code> the rate limiter will release one permit every
/// <code>(1.0 / permitsPerSecond)</code> seconds. When the rate limiter is unused,
/// bursts of up to <code>permitsPerSecond</code> permits will be allowed, with subsequent
/// requests being smoothly limited at the stable rate of <code>permitsPerSecond</code>.
/// </remarks>
/// <param name="permitsPerSecond">
/// The rate of the returned <code>RateLimiter</code>, measured in how many permits become available per second
/// </param>
public static RateLimiter Create(double permitsPerSecond)
{
/* The default RateLimiter configuration can save the unused permits of up to one second.
* This is to avoid unnecessary stalls in situations like this: A RateLimiter of 1qps,
* and 4 threads, all calling acquire() at these moments:
*
* T0 at 0 seconds
* T1 at 1.05 seconds
* T2 at 2 seconds
* T3 at 3 seconds
*
* Due to the slight delay of T1, T2 would have to sleep till 2.05 seconds,
* and T3 would also have to sleep till 3.05 seconds. */
return(Create(SleepingStopwatch.CreateFromSystemTimer(), permitsPerSecond));
}